1. Field of the Invention
The invention relates to transconductance current regulators providing an output current accurately proportional to a control voltage, i.e. voltage to current converters, and more particularly to a monolithically integrated circuit suitable for driving a motor for exerting a variable torque responsive to a voltage control.
2. Prior Art
Aircraft engine and flight controls have continued to grow in sophistication as engine requirements and flight requirements have become more complex. The solutions to these control problems have for many years been electronic, even though the ultimate response of the control system is a mechanical movement frequently controlling fluidic flow rates to an engine or using hydraulic actuation in relation to aircraft flight control surfaces. The problem of reliability has been a major concern, and that issue has been dealt with by redundancy.
The demands in an aircraft environment have been reliability, accuracy, performance, compactness, and manufactureability.
The electronic response to these demands are being met by growing use of application specific integrated circuits. The integrated circuits as a class have tended to fall into the digital category for computation, or the analog category for input/output signal processing. A less widely developed class of integrated circuits are those which may be required to possess signal processing functions and yet control significant amounts of power to an electrical motor, or as in the present application to a torque motor for an engine control. Because of the particular needs, the answer has been the creation of application specific integrated circuits (ASICs) capable of handling both kinds of requirements.
The integrated circuit process providing the answer for the present application has been the bipolar bimos (BiMOS) process in which very high impedance metal oxide semiconductor field effect transistor circuitry is combined with low impedance bipolar transistors. The MOS transistors may be used for signal processing where the current and power may be infinitesimal and the bipolar transistors may be used to supply significant amounts of power. The process is readily adapted to processing bidirectional control signals and producing bidirectional output currents to suit the needs of the engine or flight control. In such cases, the control signals may be processed by bidirectional transmission gates using complementary MOSFETs, and the power may be supplied using positive and negative voltage supplies and complementary bipolar transistors.
Granted that the latter approach is being taken, the need is present to perform the control functions with higher reliability, higher accuracy, greater performance, and greater compactness continues. Thus, the integrated circuit that achieved .+-.2% accuracy and not .+-.1%, or performed one function and not four; or required many outboarded components rather than a few, or required trimming or tuning rather than none at all becomes the target for further refinement.